Operating System course is a vital part of the Post Graduate Diploma in Computer Applications (PGDCA) curriculum. It lays the foundation for understanding the core functions of operating systems, such as process management, memory allocation, file systems, CPU scheduling, and security. These concepts are critical for students who aim to build a strong career in computer science and information technology.This book, IGNOU PGDCA MCS 203 Operating System Previous Years Unsolved Papers: Operating System Previous Years Unsolved Papers, has been compiled to provide students with an invaluable resource for their exam preparation. It brings together a collection of previous years' unsolved question papers, offering students the opportunity to practice, assess their knowledge, and develop problem-solving strategies. These unsolved papers are an excellent way to strengthen the understanding of operating system fundamentals and prepare for the types of questions likely to appear in exams.The focus of this book is to encourage self-study and independent thinking. By working through these papers, students will gain a clearer understanding of key operating system topics, improve their analytical skills, and become familiar with the exam format. We believe this compilation will help students achieve academic success and build a strong foundation in operating systems.We hope this book serves as a valuable tool for students and aids them in their journey toward academic and professional success.